Fluoroelastomer coating compositions are in wide use as industrial materials, for example for coating or impregnating textiles, fibers, metals, plastics, rubbers and other various base materials or substrates therewith, making the most of the good heat resistance, weather resistance, oil resistance, solvent resistance and chemical resistance of fluoroelastomers.
Fluoroelastomer coating compositions, when formulated as one-liquid type compositions using a polyamine as a curing agent, in particular, show poor storage stability, namely they gelate before application, so that they are generally prepared in the form of two-liquid type compositions comprising a fluoroelastomer-containing main material and a curing agent. In the case of aqueous dispersions, however, there arises a problem, namely the storage stability is easily lost due to aggregation of dispersed particles even when they are of a two-liquid type.
Fluoroelastomer coating materials generally contain an acid acceptor for trapping hydrofluoric acid formed upon crosslinking. In the art, metal oxides such as MgO have been used as acid acceptors. Meanwhile, aqueous coating compositions comprising an inorganic double compound have been proposed as ones improved in storage stability as compared with the metal oxide-containing ones (cf. e.g. Patent Document 1).
When a polyol curing type is employed for fluoroelastomer coating materials, a curing accelerator is generally used. In the art, the curing accelerator is added to the curing agent side, not to the main material side, since it is readily anticipated that the addition thereof to the main material side will produce such a problem as a deterioration in stability of the main material. In particular, in the case of aqueous fluoroelastomer coating materials of the polyol curing type, it has been a common practice to add the curing accelerator to the curing agent side according to the artisans' estimation of the possibility of the addition of the curing accelerator added to the main material side inducing the curing reaction therewith.
The use, as a curing accelerator, of a salt or complex of a basic compound with a pKa of not lower than 8 and an organic acid has been proposed for improving the storage stability of a fluoroelastomer coating composition (cf. e.g. Patent Document 2 and Patent Document 3). This coating composition is of the one-liquid type and the basic compound and organic acid are blended as such with the other components without preliminary formation of a salt or the like.
In the art, an alkylphenol-based dispersant is generally used in an aqueous dispersion of fluoroelastomer coating materials for dispersing the fluoroelastomer polymers. On recent years, however, this raw material has become suspected to be an endocrine disrupter, and compositions in which a polyoxyethylene alkyl ether is used as an alternative have been proposed (cf. e.g. Patent Document 4). However, there is a problem; polyoxyethylene alkyl ethers are inferior in dispersing ability to alkylphenol-based dispersants.
Patent Document 1: International Laid-open Publication Wo 99/07798;
Patent Document 2: International Laid-open Publication WO 98/07784;
Patent Document 3: International Laid-open Publication WO 99/43749;
Patent Document 4: International Laid-open Publication WO 00/53675.